I got curious about what it takes to build a bike frame, and I found this guys youtube videos. He has a 7 part series about building a mountain bike frame with lugged and brazed joints. You won't learn the fine points of brazing, but it gives you a good idea of what it takes. Overall it's a great series of videos. Just watch the ones labeled Bicycle frame building.
YouTube - mchimonas's Channel
YouTube - mchimonas's Channel